The present invention relates to a thermophilic enzyme having β-glycosidase activity. More particularly, the present invention relates to a thermophilic enzyme having β-glycosidase activity derived from a hyperthermophilic bacterium belonging to the genus Pyrococcus. 
β-Glycosidases are useful for hydrolysis of saccharides, DNA sequencing, conformational analysis of glycoproteins and glycolipids, and enzymatic synthesis of oligosaccharides and heterosaccharides with high optical purities. The catalytic reaction of β-glycosidases with substrates is specific with respect to the types of the monosaccharides constituting the substrates, and the optical isomerism and the position of the glycosidic linkage to be cleaved in the substrates. β-Glycosidases are also useful for the modification of sugar chains and the synthesis of oligosaccharides and polysaccharides retaining their optical stereoisomerism, as well as the synthesis of heterosaccharides (e.g., biosurfactants) due to their ability to transfer a glycoside group into a primary, secondary or tertiary alcohol. Hitherto, various types of β-glycosidases with different substrate-specificities have been found in bacteria and plants. However, since many of such β-glycosidases are derived from mesophilic organisms, they are poor in thermal resistance, and consequently are unsuitable for use in synthetic reactions under such extreme conditions that organic solvents are used simultaneously.
If a thermophilic β-glycosidase active in organic solvents is found, this can be used as an biocatalyst to develop a new procedure for synthesizing a heterosaccharide with high optical purity. In this procedure, the reverse hydrolytic reaction (i.e., synthetic reaction) is utilized which predominately occurs in the presence of an organic solvent. Under the circumstances, a novel β-glycosidase which is active under extreme conditions has been strongly demanded.